106 COKEELATION OF PHYSICAL FORCES. 



give to an electrometer the same amount of electricity as they 

 do if, whilst similarly electrified, they are kept forcibly to 

 gether. This experiment is the converse of the former one. 

 There is an advantage in electrical experiments of this class 

 as compared with those on heat, viz. that though there is no 

 perfect insulation for electricity, yet our means of insula 

 tion are immeasurably superior to any attainable for heat. 



Electricity directly produces heat, as shown in the ignited 

 wire, the electric spark, and the voltaic arc : in the latter 

 the most intense heat with which we are acquainted so in 

 tense, indeed, that it cannot be measured, as every sort of 

 matter is dissipated by it. . 



In the phenomenon of electrical ignition, as shown by a 

 heated conjunctive wire, the relation of force and resistance, 

 and the correlative character of the two forces, electricity and 

 heat, are strikingly demonstrated. Let a thin wire of plati 

 num join the terminals of a voltaic battery of suitable power, 

 the wire will be ignited, and a certain amount of chemical 

 action will take place in the cells of the battery a definite 

 quantity of zinc being dissolved and of hydrogen eliminated 

 in a given time. If now the platinum wire be immersed in 

 water, the heat will, from the circulating currents of the 

 liquid, be more rapidly dissipated, and we shall instantly find 

 that the chemical action in the battery will be increased, more 

 zinc will be dissolved, and more hydrogen eliminated for the 

 same time ; the heat being conveyed away by the water, 

 more chemical action is required to generate it, just as more 

 fuel is required in proportion as evaporation is more 

 rapid. 



Reverse the experiment, and instead of placing the wire 

 in water, place it in the flame of a spirit lamp, so that the 

 force of heat meets with greater resistance to its dissipation. 

 We now find that the chemical action is less than in the first 

 or normal experiment. If the wire be placed in other differ 

 ent gaseous or liquid media, we shall find that the chemical 



